The identification of known solar system objects (SSO) that will be observed by Gaia is a key point of the solar system object processing pipeline (CU4.SSO). It aims to associate the provisional tag assigned to observations of probably solar system objects to already known targets. At the time Gaia flies, it can be estimated that about 600,000 solar system objects (mainly small solar system objects) will be known and characterized by an orbit accurate enough to make their identification almost certain.